The answer would be a tilt meter I believe. A tilt meter is a plastic square with measures on the sides, there is a bubble of air that goes to the middle if the surface is even, the measurements on the sides tell what the tilt is, I hope this helps, though it is difficult to read :)
I think your answer would be the laser-ranging device. When my parents and I put up pictures or art canvases on the walls, we use this device. It projects a laser light that would show you a straight line across the wall or whatever medium you are putting this on. It often comes with a level inside of it, or at least ours does. It is very accurate and has assisted us a putting up several pieces of art, pictures, and curtains.
